Before you bid on a contract you need a minimum of 4 players including the MUCO.
Remember to check the omni kit salvage regulations at the end of contract. (Salvage section)
If you own a landhold, remember to collect your income at the start of a new game year.
If a contract expiration date is within 48 hours, all you need is a reputation of 1 with that employer to bid of any and all contract types.
Supplemental contracts are not subjected to reputation. As such you can take a Garrison contract with a disliked employer and then as a supplemental a Invasion contract without worrying for reputation.
If you want to take a harder contract, remember you can sub-contract units. Check the Procedures section for more information.
Try to take your next contract as close as possible to your current one. You will reduce a lot of travelling time for your unit. Otherwise your unit will have more chances to jump through the years and find itself ahead of the BTM game time.
Harder contracts are compensated very well, but also require a lot more words in order to be completed successfully.
Working for the same Employer will eventually give you the rights for a landhold. (Check the Reputation section on Landhold rules)